Ngo, J. | bioRxiv Science

bioRxiv2019

Interplay Between Short-range Attraction and Long-range Repulsion Controls Reentrant Liquid Condensation of Ribonucleoprotein-RNA Complexes

In eukaryotic cells, ribonucleoproteins (RNPs) form mesoscale condensates by liquid-liquid phase separation that play essential roles in subcellular dynamic compartmentalization. The formation and dissolution of many RNP condensates are finely dependent on the RNA-to-RNP ratio, giving rise to a window-like phase separation behavior. This is commonly referred to as reentrant liquid condensation (RLC). Here, using RNP-inspired polypeptides with low-complexity RNA-binding sequences as well as the C-terminal disordered domain of the ribonucleoprotein FUS as model systems, we investigate the molecular driving forces underlying this non-monotonous phase transition. We show that an interplay between short-range cation-{pi} attractions and long-range electrostatic forces governs the heterotypic RLC of RNP-RNA complexes. Short-range attractions, which can be encoded by both polypeptide chain primary sequence and nucleic acid base sequence, are activated by RNP-RNA condensate formation. After activation, the short-range forces regulate material properties of polypeptide-RNA condensates and subsequently oppose their reentrant dissolution. In the presence of excess RNA, a competition between short-range attraction and long-range electrostatic repulsion drives the formation of a colloid-like cluster phase. With increasing short-range attraction, the fluid dynamics of the cluster phase is arrested, leading to the formation of a colloidal gel. Our results reveal that phase behavior, supramolecular organization, and material states of RNP-RNA assemblies are controlled by a dynamic interplay between molecular interactions at different length scales.

biophysics↗

bioRxiv2018

Resource: Scalable whole genome sequencing of 40,000 single cells identifies stochastic aneuploidies, genome replication states and clonal repertoires

Essential features of cancer tissue cellular heterogeneity such as negatively selected genome topologies, sub-clonal mutation patterns and genome replication states can only effectively be studied by sequencing single-cell genomes at scale and high fidelity. Using an amplification-free single-cell genome sequencing approach implemented on commodity hardware (DLP+) coupled with a cloud-based computational platform, we define a resource of 40,000 single-cell genomes characterized by their genome states, across a wide range of tissue types and conditions. We show that shallow sequencing across thousands of genomes permits reconstruction of clonal genomes to single nucleotide resolution through aggregation analysis of cells sharing higher order genome structure. From large-scale population analysis over thousands of cells, we identify rare cells exhibiting mitotic mis-segregation of whole chromosomes. We observe that tissue derived scWGS libraries exhibit lower rates of whole chromosome anueploidy than cell lines, and loss of p53 results in a shift in event type, but not overall prevalence in breast epithelium. Finally, we demonstrate that the replication states of genomes can be identified, allowing the number and proportion of replicating cells, as well as the chromosomal pattern of replication to be unambiguously identified in single-cell genome sequencing experiments. The combined annotated resource and approach provide a re-implementable large scale platform for studying lineages and tissue heterogeneity.

genomics↗